Displaying Digital Fonts (Part 1 of 5)

In the Analogy of the Cave, by the ancient philosopher Plato, humans cannot directly see “real” things. Everything happening around them occurs behind their backs, projected onto a wall by a light that is even further behind them. These people are forced to interpret the truth in view the shadow only. Their ability to so depends on the source of light, the sharpness of the shadow, and – last but not least – the evenness of the cave’s wall.

The presentation of text onscreen may be thought of in a similar manner. Digital fonts contain the forms of the individual characters in mathematical formulas. These are abstract – you cannot “see” them. The curves and the outlines are only being calculated in the next step towards displaying the font. This step is called rasterization. Prior to being displayed in a digital medium, the mathematical formulas have to be – in the simplest scenario – carried over to a black and white pixel grid. In this process, the mathematically calculated outline is being placed over the grid like a molding tool. Putting it simply, all pixels that have their center within this molding tool will be displayed as black, while all pixels outside of it will be displayed as white.

outline manipulation, font = Apollo

This method works better with every additional pixel per character. With a high resolution RIP (Raster Image Processor) or even an average-quality laser printer, you have to scale up a lot to see the deviation from the mathematical formula. Differences between the rasterized and mathematically calculated from are not visible for the human eye.

However, foundries are much more concerned with the display quality of their digital fonts in low resolution media. These are first and foremost desktop displays. Especially small point sizes do not offer many pixels, so here the difference from the mathematical formula will be huge.

When talking about the resolution of media we talk, getting back to Plato, about the evenness of the cave on which onto shadows are displayed. In Plato’s allegory, no one has the opportunity to influence factors like the cave’s walls, the source of light, or the objects themselves. But today, everyone involved in displaying fonts is working on improvements continuously. Computer monitors are being built with smaller pixels, so that we have more pixels on hand for a finer rasterization of text. Meanwhile, the software for converting fonts into pixels is also becoming more refined. With optical illusions, we try to counteract the weaknesses of the displays. And of course, foundries optimize their fonts for the use in small point sizes in low resolution media by manipulating the mathematical formulas for specific point sizes. This manipulation is called hinting.

Computer Monitors

This overview of monitors is a brief and general one. There are too many different devices in application to being able to explain them all properly. Also, it often takes years before a new technology or device is used all around the world. However, it can be said without any hesitation that almost everyone is aiming at developing high resolution devices. These do not only display pictures more sharply and clearly, but also let typography shine. Even if this trend is foreseeable, high resolution displays featuring 200 PPI (Pixel per Inch) are mainly used in small, mobile devices. With this column, however, I want to talk about well-established desktop platforms: in other words, Windows and MacOS X. This is why I will be talking about 19–24 inch screens. In this category, the progress takes a bit longer.

Next week’s installment will be about rendering! You can read it here.

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